Yeah, I’ve suggested this also earlier (cannot find the topic though).
The only problem with this idea is - when we are dealing with envelopes that are sent to FX whenever a note is pressed - what happens when you press more than one keys?
This kind of device cannot function with polyphony so that might be the reason why this has not been implemented. Though it would be cool even if it had limitations 
Perhaps it would be selectable how the Envelope would sync - Wheter it would start playback when a note is pressed or when the pattern starts etc or start every 1/2 or so.
I think a way to get around this would simply be to allow copying of automation with selection.
Topic here…
Also, we already have the new LFO device that allmost supports this, so maybe that could be tweaked to allow keysync from certain instruments.